Fox Farm Happy Frog mediums are dial to around 6.3 right from the bag. Shoot for 6.5 to allow for any drift.
if you have a ph pen , you can check your tap water and if it is close to 7.0 it will work as the medium has oyster shell to buffer the ph.
I run water only soil grows ( dry ammended ) and use my tap source only .... no ph pen , no drama.